Title page for etd-0805117-102833


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URN etd-0805117-102833
Author Lin-Kai Weng
Author's Email Address No Public.
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Department Mechanical and Electro-Mechanical Engineering
Year 2016
Semester 2
Degree Master
Type of Document
Language zh-TW.Big5 Chinese
Title Flow Field Optimization for Atmospheric Plasma and Electrospray Dual Ion Sources and Its Applications on Pesticide Detection
Date of Defense 2017-07-26
Page Count 90
Keyword
  • thermal desorption probe
  • computational fluid dynamics
  • dual ion source
  • ambient mass spectrometry
  • pesticide residues
  • Abstract This study focuses on analyzing the characteristics of the crisscross symmetric coaxial dual ion source in order to discard the weakness of the initial design. Moreover, the optimized parameters obtained from this survey would be taken for the sample analysis. Computational fluid dynamics (CFD), a numerical analysis method to compute the flow field of the ambient dielectric discharge helium plasma, is adopted with the use of the ANSYS software. Hence, mass spectrometry is carried out to measure the total ion concentration of the helium plasma as the experimental verification. According to the experiment design of previous researchers, a crisscross symmetric coaxial glass tube is used as model to produce ambient dielectric discharge helium plasma. ANSYS is used to analyze the flow field movement of the helium jetted from the glass tube outlet as well as outputting the fluid velocity profile for observation. In order to confirm the accuracy of the analog border conditions, joss sticks are burnt to demonstrate a visualized flow field for the comparison with the simulation results. The simulation results show that the gases have maximum speed at glass tube outlet due to the low mass and the low density of helium gas, and the diffusion speed of the gas particles is drastically reduced at glass tube outlet. In order to get the optimized parameters, the glass tube outlet and capillary tube position are relocated so as to minimize the possibility of helium metastable ions flowing to the flow field. Eventually, a result of high ion intensity of 5.25×(10^10) ions/cm3 is obtained, matching to the results from the simulation and MS detection. During the previous experiment of the coaxial ESI+APCI source, the ion concentration of ESI are 2 to 3 orders higher than the ion concentration of APCI such that the signals of the nonpolar compounds are covered by the intense signal of the polar ones during the simultaneous detection. Therefore, ESI intensity is reduced by placing capillary in glass tube for 3 to 4 mm deeper to limit electrospray, moving the plasma gas outlet towards the MS inlet with 0.15 SLM flow rate, and heating the gas to 60℃ to increase plasma ion intensity. Results show that the pesticide on the surface of fruits and vegetables can be detected successfully. In addition, the polar and weak polar chemical compounds on the sample skin could also be detected simultaneously via the modified thermal desorption probe.
    Advisory Committee
  • Shin-pon Ju - chair
  • Lung-Ming Fu - co-chair
  • Cheng-Hsin Chuang - co-chair
  • Sheng-Yen Hsu - co-chair
  • Che-Hsin Lin - advisor
  • Files
  • etd-0805117-102833.pdf
  • Indicate in-campus at 99 year and off-campus access at 99 year.
    Date of Submission 2017-09-07

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